ABSTRACT
Dehydration of small fruits, such as grapes, blueberries, cranberries, cherries, and gooseberries, is restricted by the fruit outer surface (cuticle), which plays a major role in the control of transpiration, and in protecting the fruit against weather inclemencies or attacks from insects and parasites (Mazliak, 1970; Somogyi and Luh, 1986; Somogyi et al., 1996). This cuticle, if it has not been damaged, has little permeability to moisture (Suarez et al., 1984). It includes two classes of compounds: natural waxes and cutin. The waxes contain a particular kind of lipid, which is an ester of high molecular weight, resulting from the combination of a fatty acid with a long chain monoalcohol. With the exception of the wax esters, natural fruit waxes contain a mixture of hydrocarbons (paraffins and olefins), fatty acids (normal, hydroxylated, and ethylenic), ketones, alcohols, and aldehydes. All of these compounds have high molecular weights and similar physical properties, especially insolubility in water and a melting point between 40 and 100
°
C. Ursolic acid is
widespread on the surface of apples, cranberries, pears, and prunes, among other fruits. This acid is very difficult to dissolve from the fruit skin. For example, at 15
°
C one part of this acid dissolves in 88 parts of methanol, in 178 parts of ethanol (or in 35 parts of boiling ethanol), or in 140 parts of ether and is soluble in glacial acetic acid and 2% alcoholic NaOH (Mercks Index, 1983). The second layer of the fruit skin (cutin) is poorly soluble in most organic solvents, as the chains of constituents are firmly fixed by cross-polymerization in the membrane (Mazliak, 1970).
